Polyesters, particularly poly(ethylene terephthalate) (PET), are increasingly used in engineering type applications that require a combination of high modulus, high tensile strength, good surface appearance and good impact properties at ambient to low temperatures. PET possesses many desirable properties such as high modulus and high tensile strength and is generally used in applications when high notched Izod impact strength is not required. However, the poor notched Izod impact strength of polyesters like PET at 23.degree. C. and below, limits their usefulness, particularly in molding applications since these applications require good impact strength.
Many methods of improving the impact strength of PET have been tried. These methods of improving the impact strength generally entail the incorporation of a rubber such as ethylene propylene rubber (EPR) modified with highly polar groups.
U.S. 4,771,108 discloses the blend of a polyester and an incompatible polyolefin in combination with an ionomer.
U.S. 4,219,628 discloses a polyester, such as Poly(1,4-cyclohexylenedimethylene terephthalate) neat or modified, blended with EPR and an ionomer.
U.S. 4,639,481 discloses the composition containing minor amounts of a polyester such as PET and a major portion of an aromatic polycarbonate in combination with an olefin copolymer such as EPR.
U.S. 4,558,096 discloses the blend of PET and rubber blended with a compatibilizing agent such as an alkyl succinic anhydride.
U.S. 4,956,501 discloses a polyester composition containing a crosslinked blend of PET and grafted EPDM.
U.S. 4,368,295 discloses a blend of PET with a noncarboxylated polyolefin and a non-carboxylated EPR in combination with a carboxylated polyolefin.
U.S. 4,251,644 discloses the improvement of mechanical properties of nylon and polyester by blending with a rubber such as EPR that contains grafted highly polar groups.
U.S. 4,780,506 discloses a blend containing PET, aromatic polycarbonate and styrene-acrylonitrile grafted copolymers of EPDM.
U.S. 4,172,859 discloses a myriad number of combinations of blends of PET and polycarbonate containing various rubbers including maleic anhydride grafted rubber.
Although the above methods could in some instances improve the impact strength of the polyester, the resulting combination generally has poor physical properties and/or phase separates during melt injection molding. It would be very desirable to be able to produce a polyester composition such as a PET blend that has improved impact strength while retaining the polyester's good physical properties. It would also be very desirable to produce a polyester composition that has good physical properties and does not phase separate when molded.